This invention relates to a mold closing unit of an injection molding machine which includes a stationary mold clamping plate and a movable mold clamping plate slidable along parallel guide rods relative to the stationary plate, movable and fixed dies affixed to the respective plates. The mold closing unit includes a fixed, hydraulic mold closure retention cylinder, and a hydraulic traveling cylinder which includes a piston operable within the retention cylinder and being connected to the movable die. A multi-way valve is arranged in a supply line connected with the traveling cylinder, the valve being controllable for the operation of a speed pattern specified for the movable mold clamping plate.
When closing an injection mold from its open final position, i.e. at a maximum distance between the mold clamping plates, a maximum pressure acts on the traveling cylinder, and the movable mold clamping plate, with one-half the injection mold die affixed thereon, is initially accelerated and then decelerated in such a manner that the injection mold is closed at a reduced speed. The deceleration of the movable mold clamping plate is effected in such a manner that the last phase of the closing of the injection mold is effected below a predetermined creep rate. In general, the time for one injection cycle is attempted to be maintained as short as possible, i.e. the time for the production of a molded part. Thus, the movable mold clamping plate at its maximum mold opening width is given, as quickly as possible, its maximum speed from its open position, and deceleration must be effected within such a short time that the closing of the injection mold below the creep rate is still possible.
In published West German patent application No. 30 32 407, this deceleration is carried out particularly in the last phase of the closing in such a manner that deceleration is effected as a function of the kinetic energy of the movable mold clamping plate and of the movable die half affixed thereto. Since this kinetic energy is dependent on the mass of the movable mold clamping plate and of the clamped half of the mold, and since the mass of the clamped half of the mold may vary for different injection molds, such factors must be taken into account. This is accomplished by the design of the electronic circuitry which takes into consideration the injection mold half to be clamped for a given injection molding operation, so that an envelope curve takes its course, so-to-speak, electronically with a quadratic delay so that a closing below the creep rate is assured, even after a mold change. However, the technical complexity is considerable for such mold closing units so that they are generally only used for injection molding machines.